71 Engine Cooling System - Temperature High

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The coolant temperature sensor (CTS) is a thermistor located in a coolant passage on the engine. When coolant temperature is cold the sensor has a high resistance, as temperature increases the resistance of the sensor decrease. The PCM provides a five volt signal to the coolant sensor, which is also connect to PCM ground. The PCM reads the voltage drop on the signal line to determine coolant temperature.

Information Flag Parameters

Information Flag 71 will set if:

  • Engine coolant is above 118°C (239°F).

Diagnostic Aids

  • Information Flag 71 indicates higher than normal coolant temperatures. It does not indicate a faulty CTS subsystem.
  • Check engine cooling system for proper operation. Check for correct operation of fan and coolant level.

Possible causes of high coolant temperature:

  • Low coolant
  • Thermostat stuck closed
  • Reservoir cap damage
  • Hoses collapsing
  • Water pump damaged
  • Plugged radiator

NOTICE: Information flags should be used for diagnostic purposes only. They do not necessarily indicate component malfunction/failure.

NOTICE: The A/C will shut off at 118°C (244°F) to protect the engine.

NOTICE: Trailer grade loads may cause this temperature without system problems.

NOTICE: Extended high ambient idle conditions may set Flag 71 without a system problem.